UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS. 


COLLEGE  OF  AGRICULTURE. 


AGRICULTURAL  EXPERIMENT  STATION, 


PEAE  SCAB 


By  RALPH  E.  SMITH. 


BULLETIN    No.    163. 

(Berkeley,  Cal.,  December,  1904.) 


W.    W.    SHANNON. 


SACRAMENTO: 

:     :     :    superintendent  state  printing. 
1905. 


BENJAMIN  IDE  WHEELER,  Ph.D.,  LL.D.,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 

E.  W.  HILGARD,  Ph.D.,  LL.D.,  Director  and  Chemist. 

E.  J.  WICKSON,  M.A.,  Horticulturist. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

ELWOOD  MEAD,  M.S..  C.E.,  Irrigation  Engineer. 

C.  W.  WOOD  WORTH,  M.S.,  Entomologist. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Agricultural  Geologist  and  Soil  Physicist.    (Soils  and  Alkali.) 

M.  E.  JAFFA,  M.S.,  Assistant  Chemist.    (Foods,  Nutrition.) 

G.  W.  SHAW,  M.A.,  Ph.D.,  Assistant  Chemist.    (Starches,  Oils,  Beet-Sugar.) 

GEORGE  E.  COLBY,  M.S.,  Assistant  Chemist.    (Fruits,   Waters,  Insecticides.) 

RALPH  E.  SMITH,  B.S.,  Plant  Pathologist. 

A.  R.  WARD,  B.S.A.,  D.V.M.,  Veterinarian,  Bacteriologist. 

E.  H.  TWIGHT,  B.Sc,  Diploma  E.A.M.,  Viticulturist. 

E.  W.  MAJOR,  B.Agr.,  Animal  Industry. 

A.  V.  STUBENRAUCH,  M.S.,  Assistant  Horticulturist,  in  charge  of  Substations. 

WARREN  T.  CLARKE,  B.S.,  Assistant  Field  Entomologist. 

H.  M.  HALL,.  M.S.,  Assistant  Botanist. 

H.  J.  QUAYLE,  A.B.,  Assistant  Entomologist. 

GEORGE  ROBERTS,  M.S.,  Assistant  Chemist,  in  charge  Fertilizer  Control. 

C.  M.  HARING,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 

C.  A.  TRIEBEL,  Ph.G.,  Assistant  in  Agricultural  Laboratory. 

C.  A.  COLMORE,  B.S.,  Clerk  to  the  Director. 


Southern  California  Substation. 


R.  E.  MANSELL,  Foreman  of  Central  Station  Grounds. 

JOHN  TUOHY,  Patron,  ) 

-   Tulare  Substation.  Tulare. 
JULIUS  FORRER,  Foreman,  \ 

J.  E.  McCOMAS,  Patron,  Pomona, 

J.  W.  MILLS,  Superintendent,  Pomona, 

In  charge  Cooperation  Experiments  of  Southern  California, 

JOHN  H.  BARBER,  Assistant  Superintendent,  Ontario,  ) 

J.  W.  ROPER,  Patron,  ) 

„„„„„  „,      r T    T      ,  r   University  Forestry  Station,  Chico. 

HENRY  WIGHTMAN,  In  charge,      ) 

ROY  JONES,  Patron,        ) 

}■   University  Forestry  Station,  Santa  Monica. 
WM.  SHUTT,  Foreman,     \ 

H.  O.  WOODWORTH,  M.S.,  Foreman  of  Poultry  Station,  Petaluma. 


The  Station  publications  (Reports  and  Bulletins),  so  long  as  avail- 
able, will  be  sent  to  any  citizen  of  the  State  on  application. 


PEAR  SCAB. 

By  RALPH  E.  SMITH. 


Aside  from  the  effects  of  blight,  the  pear  in  California  may  be  con- 
sidered our  most  healthy  fruit  tree.  Both  in  respect  to  insect  and  fun- 
gous parasites,  as  well  as  with  regard  to  the  effect  of  natural  conditions 
unfavorable  to  the  growth  of  most  fruits,  the  pear  is  subject  to  very  few 
serious  maladies.  Its  marked  immunity,  for  instance,  against  root  knot, 
root  rot  or  "  oak  fungus  disease,"  and  sour  sap,  three  of  our  most 
common  orchard  diseases,  is  well  known,  while  its  ability  to  thrive  in 
moist,  low  spots  which  are  fatal  to  the  stone  fruits,  is  frequently  taken 
advantage  of  in  utilizing  such  places  in  peach  or  other  orchards  which 
are  not  suited  to  the  main  planting.  Similarly  with  insect  pests,  it  is 
subject  to  very  few  of  a  serious  nature. 

Our  most  common  and  only  serious  pear  troubles,  with  the  exception 
mentioned  already,  are  two:  the  codling  worm  and  pear  scab.  Both  of 
these — one  an  insect,  the  other  a  fungus — affect  the  quality  of  the  fruit 
rather  than  its  quantity  or  the  vitality  of  the  tree,  and,  while  entirely 
distinct  in  their  cause  and  nature,  are  so  closely  associated  in  their 
occurrence  and  economic  relations  that  the  practical  grower  usually 
considers  them  together  in  regard  to  methods  of  prevention  and  their 
effect  upon  the  crop. 

The  present  bulletin  aims  to  give  the  practical  results  of  some  obser- 
vations upon  the  occurrence  and  treatment  of  pear  scab  in  California, 
based  upon  the  general  practice  in  numerous  orchards  which  the  writer 
has  been  able  to  keep  under  observation  in  connection  with  other  work, 
together  with  some  special  work  along  this  line  which  has  been  carried  on 
by  growers  in  various  parts  of  the  State  in  cooperation  with  this  Experi- 
ment Station.  The  conclusions  published  are  not  to  be  regarded  as  the 
results  of  extensive  technical  investigation,  but  rather  as  a  demonstra- 
tion of  methods  of  controlling  this  disease  according  to  the  best  knowl- 
edge of  the  subject,  with  such  suggestions  for  improved  methods  as  may 
be  obtained  from  the  results  of  the  season's  wrork. 

Economic  Importance  of  Pear  Scab. — Pear  scab  is  one  of  the  most 
common  of  plant  diseases,  occurring  in  practically  all  countries  where 
the  fruit  is  grown.  Its  effects,  as  already  stated,  are  not  upon  the  life 
of  the  tree,  nor  are  they  severe  upon  the  fruit  in  respect  to  quantity;  it 
is  the  commercial  quality  or  appearance  of  the  fruit  which  chiefly 
suffers.     The  effect  of  the  disease  is  well  shown  in  the  various  figures 


4  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

illustrating  this  bulletin.  A  scabby,  corky  growth  in  certain  spots  on 
the  surface,  accompanied  by  a  distortion  or  deformation  of  the  mature 
fruit,  is  the  main  feature  of  the  disease.  Scabby  pears  are  perfectly 
sound  and  of  normal  texture  and  flavor  except  in  the  affected  parts. 
The  scab  growth  is  very  superficial,  affecting  only  the  outer  surface 
tissues,  which  are  hard  and  corky.  Such  fruit  is  perfectly  healthful  and 
in  no  way  injurious  because  of  the  disease,  yet  on  account  of  their  poor 
appearance,  color,  and  shape,  pears  which  are  badly  scabbed  are  almost 
entirely  useless  for  any  purpose,  while  if  at  all  seriously  affected  they 
are  worthless  for  shipping,  undesirable  for  canning,  and  poor  for  drying. 
In  years  of  abundant  pear  scab  in  California  unsprayed  orchards 
have  shown  losses  of  from  one  fourth  to  nearly  all  the  crop  in  market- 
able pears.  This  loss  may  be  about  equally  divided  between  the  scab 
and  the  worm,  although  either  would  be  able  alone  to  cause  it.  In  an 
average  year  California  ships,  cans,  and  dries  some  60,000  tons  of  market- 
able pears,  of  a  value,  at  $25  per  ton,  of  $1,500,000.  From  these  figures 
some  idea  may  be  formed  of  the  losses  from  pear  scab  in  the  State,  con- 
sidering, in  relation  to  the  total  tonnage  utilized  as  above,  the  further 
amount  or  proportion  rendered  entirely  unmarketable,  and  the  loss  in 
quality  on  a  large  portion  of  that  actually  sold — a  loss  representing  the 
difference  between  $40  and  $15  or  $20  per  ton  in  many  seasons. 

The  Disease. — We  have  already  described,  and  the  various  figures 
illustrate,  the  general  effect  and  appearance  of  this  disease.  It  affects 
all  varieties  of  pears  more  or  less,  but  with  considerable  difference  in 
respect  to  the  different  kinds.  The  Bartlett  is  neither  the  most  nor  the 
least  affected,  but  stands  intermediate  in  the  list.  Most  susceptible  to 
scab  are  some  of  the  later  varieties  like  Winter  Nelis  and  Easter  Beurre, 
and  also  the  little  early  pear  shown  on  the  cover  of  this  bulletin.  The 
apple  is  also  affected  by  scab,  although  not  nearly  as  much  so  in  Cali- 
fornia as  the  pear,  though  in  the  Eastern  States  both  scab  and  codling 
worm  are  worse  on  apple  than  on  Bartlett  pear. 

Whether  the  pear  and  apple  scab  fungus  are  identical  has  ever  been 
an  unsettled  question  and  still  remains  so.  The  two  are  very  similar 
in  appearance  and  structure.  Both  pear  and  apple  scab  have  increased 
decidedly  in  California  within  the  last  few  years.  In  the  Sacramento 
Valley,  particularly  toward  the  upper  end  and  east  side,  pear  scab  is 
reported  to  have  been  troublesome  only  since  the  beginning  of  the  present 
decade,  while  apple  scab  is  not  yet  abundant  in  the  State,  but  is  increasing 
in  the  Santa  Cruz  and  southern  California  mountains.  The  prevalence 
of  pear  scab  shows  a  marked  relation  to  the  climatic  conditions  of  various 
parts  of  the  State  and  of  different  seasons.  The  disease  is  greatly 
favored  by  atmospheric  moisture  in  the  spring.  Sections  with  the  pre- 
vailing dry  winds  show  less  pear  scab,  and  in  seasons  with  little  spring 
moisture  the  disease  is  less  abundant  than  when  the  contrary  is  true. 


PEAR    SCAB.  O 

The  first  appearance  of  the  scab  may  be  seen  upon  the  young  pears 
or  leaves  when  the  fruit  is  quite  small.  It  appears  as  brownish  velvety 
spots  or  patches  upon  the  surface.  (See  illustration  on  cover.)  In  some 
seasons  many  pears  drop  from  the  tree  when  as  large  as  small  cherries, 
and  on  examination  may  be  found  to  be  covered  with  scab  fungus, 
though  the  dropping  is  more  often  ascribed  to  other  causes  by  those 
unfamiliar  with  the  disease.  Scab  upon  the  leaves  is  especially  marked 
in  the  Winter  Nelis.  The  spots  appear  upon  the  under  side,  often  in 
abundance,  and  are  readily  seen  and  recognized  by  the  dark  color  and 
evident  fungous  growth  of  a  velvety,  mold-like  nature.  Upon  the  young 
pears  similar  spots  appear,  as  in  the  cover  illustration  and  Fig.  1. 

This  brownish  growth  consists  of  the  pear-scab  fungus  (Fusicladium 
pirinum,  Lib.).     Its  microscopic  structure  is  shown  in  Fig.  2,  represent- 


Fig.  1.    Young  Bartlett  Pears  with  scab. 

ing  a  section  through  a  scab  spot  on  the  surface  of  the  fruit.  The  dark- 
colored  fungous  growth  occurs,  as  shown  here,  mostly  in  the  outer 
cuticle  or  extreme  surface  layer,  penetrating  very  slightly  into  the 
interior.  The  velvety  growth  on  the  surface  consists  of  numerous  erect 
threads,  which  grow  up  from  the  surface  stratum.  At  the  ends  of  these 
threads  the  oval-shaped  spores  are  produced,  which  drop  off  very  readily 
and  serve  to  distribute  the  fungus.  These  spores  are  capable  of  sprout- 
ing when  moisture  reaches  them,  and  starting  the  fungus  anew.  Pear 
scab  fungus  also  develops  upon  the  bark  of  the  young  shoots  and  twigs 
of  the  tree,  as  well  as  upon  the  fruit  and  leaves,  though  here  it  is  incon- 
spicuous and  not  as  readily  observed  as  in  the  latter  situations.  This 
fact  is  of  particular  importance  in  California  in  combating  the  disease. 
As  the  season  progresses  and  moisture  becomes  less  abundant  the 
visible  fungous  growth  upon  the  scabby  spots  become  less  prominent, 


6 


UNIVERSITY    OF   CALIFORNIA— EXPERIMENT   STATION. 


and  in  the  Bartlett  disappears  almost  entirely.  Considering  this  variety 
alone  we  find  that  as  the  fruit  swells  the  growth  of  those  pears  having 
scab  on  one  side  is  checked  in  such  places,  so  that  as  the  other  side 
enlarges  the  pear  twists  and  doubles  over,  as  in  Figs.  3  and  4;  or  even 
much  worse  than  this.  Comparing  the  mature  Bartlett  pears  in  Figs. 
3  and  4,  with  the  young  ones  in  Fig.  1,  the  nature  of  this  effect  is  readily 
seen.  In  the  same  comparison  we  see  the  brown  fungous  growth  on  the 
young  pears,  while  upon  the  older  ones  it  has  almost  entirely  disap- 
peared, leaving  only  the  scabby,  corky  appearance  of  the  surface.  This 
is  characteristic  in  California  with  the  Bartlett,  showing  that  the  scab 
on  the  mature  fruit  starts  in  the  spring,  and  that  later  infection  during 


Fig.  2.    Section  of  Scab  Spot  on  fruit,  showing  fungous  growth;  much  enlarged. 


the  summer  when  the  pears  are  nearly  grown  does  not  occur,  the  surface 
being  smooth  and  free  from  scab  except  in  the  old  original  spots.  On 
the  Winter  Nelis,  Clairgeau,  and  Easter  Beurre,  new  scab  spots  develop 
later  in  the  summer  when  the  pears  are  quite  large,  and  brown  spots  of 
fungus  can  be  seen  on  the  surface  of  these  pears,  without  much  distor- 
tion, when  the  original  spots  have  reached  the  condition  shown  in  Figs. 
3  and  4.  This  difference  in  the  time  of  infection  is  of  practical  impor- 
tance in  controlling  the  disease. 

In  Bartlett  pear  orchards  severely  affected  by  scab  the  fruit  has  been 
seen  to  average  as  bad  as  Figs.  3  and  4  for  the  whole  crop,  while  many 
of  the  pears  were  much  more  distorted,  not  to  mention  the  worms.    Such 


PEAR   SCAB.  ^ 

fruit  is  practically  worthless  and  only  a  source  of  dissatisfaction  to  all 
who  handle  it.  When  first-quality  Bartletts  are  in  demand  at  $40  per 
ton  for  the  very  best,  such  stuff  as  this  is  wanted  by  no  one  at  any 
price. 

Returning  to  the  consideration  of  the  scab  fungus,  we  find  at  the 
end  of  the  season  that  it  is  present  in  the  orchard  in  three  places:  upon 
the  leaves,  upon  any  scabby  fruit  that  remains,  and  on  the  young 
twigs.  The  condition  of  the  fungus  is  about  that  represented  in  Fig.  3. 
The  visible  surface  growth  has  died  away;   but  in  the  corky  scab-tissue, 


Fig.  3.    Scab  on  Bartlett  Pear. 

or  the  surface  layers  of  the  leaf  or  bark,  the  fungous  growth  is  still  pres- 
ent and  capable  of  further  growth,  although  in  a  dormant  condition. 
The  case  is  quite  analogous  to  that  of  many  California  weeds,  which 
flourish  in  the  moist  springtime,  then  die  down  and  disappear  from 
sight  in  summer,  but  still  exist  by  roots  and  seeds  in  the  soil  and  spring 
up  into  life  again  when  the  season  of  required  moisture  and  tempera- 
ture comes  around. 

In  winter  the  scab  fungus  exists  and  lives  through  the  season  upon  the 
dead  leaves  on  the  ground  and  in  its  growth  upon  the  bark  of  the  twigs, 
and  it  is  from  these  sources  that  it  starts  again  next  spring.     The  spores 


8 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


of  the  fungus  have  no  apparent  relation  to  its  hibernation,  since  they 
sprout  with  the  first  moisture  and  are  very  sparingly  produced  after  the 
early  summer.  It  is  rather  the  dormant  growth  in  the  leaf  and  twig- 
bark  tissues  which  lives  over,  starting  into  growth  and  producing  new 
crops  of  spores  next  spring. 

The  question  as  to  the  relative  importance  of  the  old  leaves  on  the 
ground  and  the  bark  of  the  tree  itself  as  a  source  of  scab  in  spring  is  of 
the  greatest  practical  importance.  There  is  no  question  that  the  fun- 
gus does  exist  in  both  situations,  so  that  a  study  of  this  in  itself  gives 


Fig.  4.    Scab  on  Bartlett  Pear. 


little  light  on  the  essential  question.  The  practical  results  of  experi- 
ments in  treating  the  disease,  however,  as  brought  out  in  a  later  chapter, 
seem  to  indicate  quite  plainly  that  infection  takes  place  in  the  spring 
from  the  bark  scab  on  last  year's  growth,  rather  than  from  the  old 
leaves.     This  will  be  more  fully  considered  elsewhere. 

CONTROL  OF  PEAR  SCAB. 

That  pear  scab  may  be  effectually  controlled  by  proper  and  well- 
timed  spraying  has  been  repeatedly  demonstrated  in  many  parts  of  the 
country.      That  it  is  not  controlled  in  a  great  many  California  pear 


PEAR    SCAB.  9 

orchards,  in  many  cases  even  where  more  or  less  spraying  is  done  for 
this  particular  purpose,  is  but  too  well  known  to  all  who  handle  the 
crop.  The  object  of  this  work  was  therefore  primarily  to  find  the  reason 
for  the  failure  of  much  well-meant  work  which  is  done,  and  to  point  out 
the  best  and  most  economical  practice  for  use  under  California  condi- 
tions. In  other  words,  more  definite  information  was  needed  as  to  what 
is  effective  and  essential  in  the  control  of  this  pest,  and  what  is  non- 
effective and  useless  in  regard  to  present  practice. 

The  usual  recommendations  for  pear-scab  treatment,  published  in 
bulletins  and  spray  calendars  of  the  various  State  experiment  stations, 
call  for  spraying  with  Bordeaux  mixture  just  as  the  buds  expand,  again 
after  the  blossoms  have  fallen,  and  a  third  time  about  two  weeks  later. 
This  refers  to  spraying  for  scab  alone,  without  reference  to  insect  pests. 
In  California  the  spraying  of  pears  for  scab  has  been  largely  along  the 
line  of  general  treatment  for  the  eradication  of  all  pests,  definite  or 
indefinite.  To  "clean  up  the  tree"  is  a  popular  expression  of  the  object 
of  most  pear-tree  spraying,  except  the  use  of  paris  green  for  worms. 
More  definitely  stated,  the  usual  California  practice  of  pear  spraying 
consists  in  treatment  with  lime,  sulfur  and  salt  in  January  for  scale, 
scab,  moss,  softening  the  bark,  and  a  general  "clean  up."  This  is 
applied  by  some  every  year,  by  others  once  in  two  or  more  years,  and  in 
still  other  cases  not  at  all.  Beyond  this  two  or  three  sprayings  with 
paris  green  and  lime  are  made  in  summer  after  the  fruit  sets,  adding 
bluestone  for  scab  and  general  results. 

The  results  of  this  treatment  have  not  been  entirely  satisfactory  in 
relation  to  scab  control.  While  the  disease  has  varied  in  abundance 
from  year  to  year,  orchards  sprayed  in  this  way  have  shown  much  scab 
in  years  when  it  was  abundant  and  considerable  losses  have  resulted. 
Neither  the  early-winter  lime,  sulfur  and  salt  treatment,  or  the  summer 
paris  green,  bluestone,  and  lime  spray,  or  the  combination  of  the  two, 
has  shown  decidedly  satisfactory  results  in  scabby  seasons  when  closely 
followed  up,  although  such  treatment  has  been  better  than  none  at  all. 

In  spraying  orchards  year  after  year  for  some  time  it  naturally 
results  that,  on  account  of  varying  weather  conditions  and  other  causes, 
the  work  is  not  done  at  the  same  time  every  year.  This  has  been  the 
case  in  the  winter  spraying  of  pear  trees  with  lime,  sulfur  and  salt. 
The  time  of  such  treatment  has  thus  varied  from  December  to  the  time 
of  blossoming  in  March,  in  different  orchards  and  in  different  years  in 
the  same  orchard.  Various  other  sprayings  have  also  been  done  in  a 
variety  of  instances,  differing  more  or  less  from  the  usual  practice  out- 
lined above.  From  such  sources  there  seemed  to  have  been  demon- 
strated, in  a  number  of  instances  in  this  State,  that  spraying  at  some 
period  just  before  the  time  of  blossoming  was  particularly  effective  in 
the  control  of  scab.     One  grower,  for  instance,  in  spraying  with  lime, 


10  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

sulfur  and  salt,  was  delayed  by  rainy  weather  so  much  that  in  one 
block  the  buds  were  much  advanced  and  the  spraying  not  done. 
Finally  a  last  tankful  was  put  on  when  the  trees  were  almost  in  full 
bloom  and  the  remainder  of  the  block  left  unsprayed.  Although 
many  blossoms  were  killed  by  such  late  treatment  with  this  caustic 
spray,  the  effect  on  scab  was  most  decided,  the  trees  receiving  the  late 
treatment  producing  very  much  cleaner  fruit  than  those  sprayed  earlier 
in  the  winter  or  those  not  sprayed  at  all.  This  incident  is  typical  of  many 
similar  ones  which  might  be  cited.  Such  experience  goes  further  than 
to  support  the  usual  recommendation  of  spraying  as  the  buds  unfold, 
representing  one  of  three  or  more  applications,  since  it  appears  to  indi- 
cate the  existence  of  a  time  when  one  spraying  is  peculiarly  effective 
under  California  conditions,  or  when  more  than  one,  close  together, 
might  be  more  effective  than  the  same  number  at  any  other  time. 

With  this  idea  in  mind  the  cooperative  work  carried  on  during  the 
past  season  was  instituted.  The  plan  was  to  find  out,  by  spraying  at 
various  definite  times,  the  most  effective  period  of  spraying  for  scab 
control,  and  in  general  the  comparative  effect  of  treatment  at  various 
times  before  and  after  the  setting  of  the  fruit.  Particular  arrangements 
were  made  for  such  work  with  Mr.  Fred  Cottle  of  the  O'Toole  ranch, 
San  Jose,  and  Mr.  D.  Z.  Hawkins  of  the  Aloha  Fruit  Farm,  Anderson, 
and  to  the  active  efforts  of  these  gentlemen  in  carrying  out  the  work  as 
planned,  in  spite  of  extremely  unfavorable  weather  conditions,  is  due  in 
a  large  measure  the  value  of  the  results  contained  in  this  bulletin. 
Some  cooperative  work  was  also  done  with  Mr.  Edward  Rider,  of  Sac- 
ramento, and  Mr.  Frank  Tupper,  of  Newcastle,  while  the  active  pro- 
motion of  scab  treatment  in  many  orchards  carried  out  through  the 
enterprising  spirit  of  the  California  Fruit  Canners'  Association,  by  their 
representative,  Mr.  Geo.  W.  Pratt,  was  another  source  of  much  valuable 
information.  Observations  were  also  made  in  numerous  orchards  of 
the  results  of  various  treatments  carried  out  according  to  the  ideas  of 
their  owners. 

EXPERIMENTAL  WORK. 

Work  at  the  O'Toole  Ranch. — Mr.  Cottle's  orchard,  which  received 
treatment,  consisted  of  Bartletts,  Winter  Nelis,  Ciairgeaus,  Easter 
Beurres,  and  Vicars,  giving  a  long  range  of  blossoming,  various  degrees 
of  susceptibility  to  scab,  and  conditions  generally  very  favorable  to  a 
study  of  this  sort.  The  time  of  spraying,  in  this  and  all  the  work  done, 
was  gauged  by  the  opening  of  the  buds.  Figs.  5,  6,  7,  8,  and  9  represent 
typical  stages  in  the  opening  of  pear  buds:  the  first  swelling  of  the 
whole  bud,  the  expansion  of  the  leaves  and  separate  flower  buds,  and 
final  opening  of  the  single  blossoms.  Each  fruit  bud,  as  seen  from  the 
illustrations,  develops  several  leaves  and  a  cluster  of  blossoms,  though 
the  figures  do  not  all  represent  the  same  variety  of  pear.     In  the  Winter 


PEAR    SCAB. 


11 


Nelis  and  the  earlier  blooming  varieties  most  of  the  blossoms  open  at 
about  the  same  time  (as  in  Fig.  8),  so  that  the  whole  orchard  comes 
suddenly  into  full  bloom.  The  Bartlett  straggles  along  in  blooming, 
like  Fig.  9,  some  blossoms  opening  a  month  ahead  of  others.  The  dates 
of  full  bloom  for  the  varieties  present  on  the  O'Toole  ranch  were  about 
as  follows  in  1904:  Clairgeau,  March  29;  Easter  Beurre,  April  1;  Vicar, 
April  6;  Winter  Nelis,  April  8;  Bartlett,  April  15. 

The  following  table  gives  a  general  resume  of  Mr.  Cottle's  spraying, 
using  Bordeaux  mixture  with  5  pounds  of  bluestone,  6  pounds  of  lime, 


Fig.  5.    First  stage  in  bud  develop- 
ment.   Slightly  swollen. 


Fig.  6.    Second  stage  in  bud  development. 


and  50  gallons  of  water,  with  no  previous  spray  of  any  sort  during  the 
winter: 


Date.  Variety 

March  15 Clairgeau 


No.  of  Rows,  etc. 


All. 


Buds,  as  in 
-   Fig.  7 
6-7 
9 


March  16.. Easter  Bern-re" 4  rows 

March  25 Easter  Beurr6 4  rows,  second  time- 
March  25 ...  Easter  Beurre* 2  rows,  first  time. ... 

March  25 Winter  Nelis 4  rows,  first  time 

March26 ...  Clairgeau.   ....   All,  second  time "    9 

March  27 Winter  Nelis.. .   ....  7  rows,  first  time "    8 

March  27 Vicars All 

April    16 Bartlett All 

May       1... All  varieties -._ All,  but  checks  sprayed 

with     Bordeaux     and 

Paris  Green Passed  bloom. 

Later  spraying  with  Bordeaux  and  Paris  Green. 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

This  table  summarizes  as  well  as  possible  all  the  spraying  done  at  this 
place.  Check  trees  were  left  of  most  varieties,  so  that  the  amount  of 
scab  normally  developed  could  be  seen  and  the  gain  by  spraying  thereby 
estimated.  Considering  the  various  varieties  the  record  may  be  better 
understood  by  saying  that  the  Clairgeaus  were  sprayed  twice  before  the 
blossoms  opened:  once  when  in  the  stage  of  Fig.  7,  and  again  ten  days 
later  when  as  in  Fig.  9  or  partially  in  bloom.  After  the  fruit  was  well 
set  they  were  sprayed  again,  and  still  further  later  in  the  summer, 
adding  paris  green  after  the  blossoms  had  fallen.  Of  the  six  rows  of 
Easter  Beurres,   four  rows   were   treated  the  same  as  the   Clairgeaus, 


Fig.  7.    Third  stage  in  bud  development. 

with  two  sprays  before  the  blossoms  opened,  while  two  rows  did 
not  receive  the  first  spraying  at  the  third  stage  (Fig.  7) .  All  received 
the  combined  later  sprays  (except,  as  should  be  understood  in  every  case, 
the  unsprayed  check  trees).  Of  the  Winter  Nelis  a  part  were  sprayed 
once  at  the  fourth  stage  (Fig.  8),  and  all  after  the  fruit  set.  The  Vicars 
were  all  sprayed  once  when  nearly  in  bloom  and  several  times 
later  like  the  others.  The  Bartletts  were  all  sprayed  when  at  the  fifth 
stage  (Fig.  9),  and  later  as  with  all  the  rest.  In  several  cases 
individual  trees  were  sprayed  when  in  full  bloom,  but  it  could  not  be  seen 
that  this  had  any  injurious  effect  upon  the  setting  of  the  crop. 

The  results  of  this  work  were   quite  instructive.      While    a  decided 


PEAR    SCAB. 


13 


gain  was  apparent  from  all  the  spraying  done  before  the  blossoms  opened, 
there  was  still  considerable  scab  on  several  of  the  varieties  and  the  fruit 
was  not  as  clean  as  could  be  desired.  The  Bartletts  and  Winter  Nelis, 
for  instance,  sprayed  once  just  before  the  blossoms  opened,  and  several 
times  later,  gave  a  crop  of  very  good  quality,  yet  not  as  free  from  scab 
as  could  be  desired. 

The  Easter  Beurres  seemed  to  demonstrate  very  plainly  the  secret  of 
the  most  successful  scab  control.     The  four  rows  of  this  variety  sprayed 


Fig.  8.    Fourth  stage  in  bud  development. 

twice  before  the  blossoms  opened,  as  in  Figs.  6  and  9,  bore  fruit  very  free 
from  scab,  while  on  the  check  trees  almost  every  pear  was  scabby.  The 
rows  sprayed  once  in  the  fifth  stage  (Fig.  9)  were  better  than  the 
unsprayed,  but  much  more  scabby  than  those  which  had  the  earlier 
treatment.  Moreover,  a  few  trees  which  had  the  first  spray  but  not  the 
second,  were  much  cleaner  than  those  which  had  the  second  alone,  and 
nearly  as  good  as  the  four  rows  which  had  both.  The  difference  in  this 
scab-susceptible  variety  was  very  marked  in  favor  of  the  earlier  spray, 


14  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

while  with  the  two  sprayings  before  the  blossoms  opened,  the  results 
were  the  best  of  any  obtained  in  the  whole  work. 

The  Clairgeaus,  all  of  which  received  these  two  treatments,  were  also 
very  clean  and  free  from  scab.  In  some  cases,  as  with  part  of  the  Win- 
ter Nelis  and  various  single  trees  of  other  varieties,  no  spray  was  put 
on  until  after  the  blossoms  fell  and  the  fruit  had  set.  In  these  little 
gain  could  be  seen  over  trees  unsprayed  the  whole  season.  Spraying 
after  the  fruit  set,  with  no  previous  treatment,  had  almost  no  effect 
on  the  amount  of  scab. 

The  fact  already  mentioned  in  connection  with  the  development  of 
scab  on  the  different  varieties  was  quite  marked  in  this  orchard,  namely, 
that  on  the  Bartletts  the  injury  to  the  fruit  was  caused  by  scab  which 
started  with  the  fruit  from  the  first,  and  no  new  spots  developed  in  sum- 


Fig.  9.    Fifth  stage  in  bud  development.    Blossoms  beginning  to  open. 

mer,  while  with  some  of  the  later  varieties  new  scab  spots  developed  on  the 
fruit  after  it  had  attained  considerable  size.  This  fact  in  connection  with 
the  Bartlett,  and  the  decided  effect  with  other  varieties  of  checking  the 
development  of  the  fungus  so  thoroughly  by  a  single  early  spraying,  both 
indicate  an  important  fact  in  regard  to  the  origin  of  scab  in  the  spring. 
If  spores  from  the  dead  leaves  on  the  ground  were  the  principal  source 
of  infection  neither  of  these  facts  would  be  expected  to  hold  true,  as  the 
fungus  would  of  necessity  gradually  work  up  into  the  tree  tops.  The 
fact  that  it  has  a  definite  brief  time  of  development,  occurring  simulta- 
neously with  the  development  of  the  pear  buds,  and  that  spraying  at 
this  time  checks  the  fungus  for  the  whole  season,  suggest  very  strongly  a 
development  of  scab  upon  the  twigs  and  fruit  spurs  when  growth  starts 
in  the  spring  rather  than  infection  by  spores  from  the  ground.     (The 


PEAR    SCAB.  15 

same  holds  true  for  peach  curl,  sycamore  blight  and  all  such  tree  dis- 
eases, which  make  a  sudden  start  in  spring,  simultaneous  on  all  the 
trees  and  all  parts  of  each  tree,  and  where  the  fungus  is  known  to  infect 
the  twigs.) 

Work  at  Anderson. — At  the  Aloha  Fruit  Farm,  of  which  Mr.  Hawkins 
is  manager,  there  are  about  twenty  acres  of  pear  trees,  all  Bartletts. 
Work  was  started  here  along  the  same  general  line  as  at  San  Jose,  to 
determine  the  most  effective  time  for  spraying  in  the  control  of  scab. 
The  disease  has  increased  greatly  in  this  section,  coming  into  prom- 
inence only  within  a  very  few  years.  Bordeaux  mixture  of  the  same 
formula  as  in  the  other  work  was  used  here,  adding  paris  green  for 
worms  after  the  fruit  set.  Little  account  of  these  later  sprayings  is 
taken  in  this  bulletin  in  any  instance,  as  the  problem  of  worm  control 
does  not  come  within  the  scope  of  this  work. 

Mr.  Hawkins  sprayed  his  whole  orchard,  with  the  exception  of  two 
rows,  just  before  the  blossoms  opened,  or  at  about  the  fourth  stage  (Fig. 
8).  After  the  fruit  had  set  he  sprayed  again,  including  this  time  one  of 
the  two  rows  omitted  before.  Thus  the  bulk  of  the  orchard  was  sprayed 
twice:  once  before  and  once  after  the  fruit  had  set;  one  row  was  sprayed 
once,  at  the  latter  time,  and  the  last  row  was  not  sprayed  at  all. 
Examined  on  June  13,  the  following  notes  were  made  by  the  writer: 
"  Scab  abundant  on  last  row.  Nearly  as  bad  on  row  sprayed  once; 
very  little  difference,  if  any.  Scarcely  any  on  remainder."  Here  again 
was  evident  the  decided  effect  of  spraying  shortly  before  the  blossoms 
opened  and  the  lack  of  effect  of  later  spraying  upon  scab  development. 

Had  the  comparative  amount  of  scabby  fruit  been  calculated  and 
the  difference  in  value  estimated,  the  one  early  spraying  in  this  orchard 
would  show  an  amount  of  saving  beside  which  the  cost  of  the  operation 
would  be  insignificant.  Yet  had  the  first  spraying  been  postponed  for 
two  weeks  or  less,  and  the  same  amount  of  work  done,  and  done  just 
as  thoroughly,  later  in  the  season,  no  result  whatever  would  have  been 
evident,  as  shown  by  the  abundance  of  scab  on  the  late-sprayed  row. 
In  fact,  so  far  as  the  effect  on  scab  is  concerned  the  experiment  shows 
that  the  second  spraying  of  the  whole  orchard  had  very  little  effect,  and 
could  have  been  omitted  altogether  or  done  more  profitably  at  about  the 
second  stage  (Fig.  6),  making  the  two  sprays  at  the  second  and  fifth 
stages  of  bud  development  (Figs.  6  and  9).  If  spraying  for  worms  is 
done  just  after  the  fruit  sets  there  is,  of  course,  but  very  little  extra 
expense  in  adding  bluestone  and  lime  to  make  a  Bordeaux  mixture,  and 
this  will  do  no  harm  and  perhaps  a  little  good.  No  winter  spraying 
was  done  in  the  Hawkins  orchard  previous  to  the  Bordeaux  spray. 

Work  at  Sacramento. — Mr.  E.  Rider  at  Sacramento  had  a  Bartlett 
pear  orchard  of  which  the  trees,  on  one  side  particularly,   had  been 


16  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

affected  by  scab.  Spraying  of  this  orchard  was  greatly  interfered  with 
on  account  of  the  wet  condition  of  the  soil,  but  part  of  it  was  sprayed 
in  winter  with  lime,  sulfur  and  salt.  As  the  buds  were  swelling 
and  before  the  blossoms  opened,  the  rows  on  the  side  worst  affected  by 
scab  in  previous  years  were  sprayed  twice  with  Bordeaux  mixture,  and 
once  after  the  fruit  set.  The  result  a  few  weeks  later  was  very  marked 
in  this  orchard.  The  usual  condition  was  reversed:  the  sprayed  rows  on 
the  previously  scabbiest  side  having  very  clean  fruit,  while  the  unsprayed 
and  usually  cleanest  rows  were  much  the  worst.  This  again  was  a  very 
striking  proof  of  the  effectiveness  of  proper  spraying  for  this  disease. 

Work  at  Newcastle. — Mr.  Frank  Tupper  of  Newcastle  sprayed  some 
pear  trees  according  to  arrangements  made  for  testing  the  matter  in  that 
section.  A  block  of  Bartletts  in  his  orchard,  without  previous  treatment, 
were  sprayed  with  Bordeaux  mixture  just  as  the  blossoms  were  opening, 
the  bulk  of  the  orchard  receiving  lime,  sulfur  and  salt  in  March,  before 
the  buds  had  started  or  swollen  much,  and  all  being  sprayed  with 
Bordeaux-paris  green  after  the  fruit  had  set.  None  of  this  spraying  suc- 
ceeded in  controlling  the  scab  fungus  very  effectually.  The  fruit  in  the 
trees  sprayed  specially  with  Bordeaux  was  scarcely  better  than  that  on 
unsprayed  trees.  Apparently  the  lime,  sulfur  and  salt  treatment  was 
too  early  and  the  Bordeaux  too  late  for  the  best  results  in  scab  con- 
trol. Mr.  Tupper  carried  on  the  work  faithfully  according  to  directions, 
and  this  negative  result  is  no  less  valuable  in  demonstrating  the  most 
effective  time  for  scab  control  than  those  in  which  more  saving  was 
accomplished. 

Work  in  other  Orchards. — In  various  orchards  the  writer  has  followed 
the  effect  on  scab  of  spraying  with  lime,  sulfur  and  salt,  before  the  fruit 
buds  swell.  In  one  case,  for  instance,  part  of  the  orchard  was  left 
unsprayed,  the  work  stopping  part  way  down  a  row  of  Winter  Nelis. 
This  was  in  February.  In  the  amount  of  scab  next  summer  no  differ- 
ence could  be  seen  in  this  row  or  in  the  sprayed  and  unsprayed  parts  of 
the  whole  orchard.  All  were  equally  scabby.  Many  similar  instances 
of  this  could  be  cited,  all  showing  that  while  winter  spraying  with  lime, 
sulfur  and  salt  kills  scale  when  present,  cleans  up  the  trees  and 
improves  their  appearance  and  condition  generally,  its  actual  effect 
upon  scab  the  next  season  is  very  slight.  It  is  apparently  too  early  to 
catch  the  fungus  in  an  active  condition,  and  this  fails  to  prevent  its 
later  development.  This  spray  would  no  doubt  be  equally  effective 
with  the  Bordeaux  mixture  could  it  be  used  safely  as  late  in  the  season. 
It  has,  however,  no  advantage  over  the  latter  as  a  fungicide,  so  that 
each  is  best  in  its  own  place  in  the  spray  calendar. 

Spraying  for  scab  after  the  fruit  sets  may  be  dismissed  with  equal 
brevity.     With  some  of  the  later  varieties  this  may  have  some  effect  in 


PEAR   SCAB.  17 

checking  the  summer  development  of  scab,  and  in  any  case  the  expense 
of  adding  bluestone  to  the  codling  worm  spray  is  so  small  that  for  the 
general  purpose  of  keeping  down  the  scab  fungus  in  the  orchard  as 
much  as  possible  all  the  year  round  it  is  advisable  to  make  a  Bordeaux 
mixture  of  the  arsenical  spray.  This  late  treatment,  in  itself,  however, 
has  in  every  instance  been  shown  to  be  of  absolutely  no  effect  in  keep- 
ing down  scab  in  Bartletts,  in  the  crop  of  the  season,  and  were  it  not 
for  the  worm-spray  combination  could  probably  be  omitted  with  profit. 
The  failure  of  the  ordinary  practice  of  spraying  with  lime,  sulfur  and 
salt  in  winter,  and  arsenical  Bordeaux  in  summer  for  scab  control,  is 
thus  seen  to  come  about  because  the  former  is  too  early  and  the  latter 
too  late.  The  present  wrork  indicates  that  a  crop  of  scab  develops  from 
dormant  fungous  growth  on  the  fruit  spurs  and  twigs  just  as  the  buds 
open,  that  this  infects  the  fruit  when  very  young,  and  that  the  most 
effective  spraying  destroys  this  growth  before  the  blossoms  develop  or 
infection  takes  place,  rather  than  protecting  the  young  fruit  when  formed. 

DIRECTIONS  FOR  SPRAYING  PEARS  TO  CONTROL  SCAB. 

(To  be  combined  in  the  various  localities  with  the  best  known  practice 
for  codling  worm  control.) 

1.  Plow  under  or  clean  up  the  dead  leaves  in  the  fall  as  much  as 
possible. 

2.  For  very  thorough  results,  spray  with  lime,  sulfur  and  salt  every 
other  year  as  late  in  winter  as  possible. 

3.  Spray  with  Bordeaux  mixture  twice  while  the  buds  are  unfolding 
beginning  the  first  time  (with  formula  A)  when  the  buds  are  in  the 
second  stage  of  development  as  in  Fig.  6,  the  second  (with  formula  B) 
when  as  in  Fig.  7,  or  about  a  week  or  ten  days  apart.  Remember  that 
the  idea  is  to  kill  the  scab  developing  on  the  bark  as  the  buds  swell,  and 
not  on  the  young  pears  after  they  have  formed.  For  a  single  treatment 
the  early  Bordeaux  spray  is  most  effective. 

4.  Begin  the  spraying  in  large  orchards  as  early  as  the  second  stage 
of  bud  development,  as  in  Fig.  6,  so  that  if  delays  occur  the  trees  will 
get  at  least  one  spraying  before  it  is  too  late.  Before  the  first  (Fig.  5)  or 
after  the  fourth  stage  (Fig.  8),  very  little  direct  good  can  be  done  on  the 
present  year's  scab  by  any  treatment,  especially  with  Bartletts. 

5.  Add  bluestone  to  the  paris  green-lime  spray  used  against  worms 
for  general  results,  especially  with  the  later  varieties  of  pears. 

FORMULAS. 

Bordeaux  Mixture. — 

(A)     Bluestone... 8  lbs.  (B)    Bluestone 5  lbs. 

Quicklime 10  lbs.  Quicklime   7  lbs. 

Water 50gals.  Water 50  gals. 


18  UNIVERSITY    OF    CALIFORNIA— EXPERIMENT    STATION. 

Dissolve  the  bluestone  and  slake  the  lime  in  separate  barrels.  Strain 
the  bluestone  into  the  spray  tank;  make  up  to  about  40  gallons,  then 
strain  in  the  lime  mixed  with  the  remaining  10  gallons  of  water.  If 
the  two  materials  are  mixed  outside  of  the  spray  tank,  each  should 
first  be  well  diluted.  Stock  solutions  of  bluestone,  1  pound  to  1  gallon, 
can  be  kept  indefinitely. 

Lime,  Sulfur  and  Salt. — 

Lime - -._ _.. _ 40  lbs. 

Sulfur 20  lbs. 

Salt 15  lbs. 

Water..- ._. 60  gals. 

Slake  the  lime,  add  the  other  ingredients,  boil  from  one  to  two  hours, 
strain,  and  apply  while  hot.  This  is  the  usual  formula,  although  some 
use  considerably  less  of  the  ingredients. 

A  method  of  cooking,  as  follows,  is  also  finding  considerable  use: 
Make  the  sulfur  into  a  paste  with  hot  water,  place  the  lumps  of  lime 
in  a  tight  cask,  pour  on  the  sulfur,  and  add  10  or  15  gallons  of  boil- 
ing water.  The  cask  is  then  covered  tightly  with  sacks  and  a  wooden 
cover,  and  an  extremely  violent  boiling  takes  place.  When  this  begins 
to  subside  the  mixture  is  stirred  thoroughly  and  after  all  boiling  stops 
it  is  strained  into  the  spray  tank,  the  salt  having  been  added,  with 
enough  more  boiling  water  to  make  up  the  required  quantity.  For  gen- 
eral purposes  this  self-boiled  mixture  appears  to  be  satisfactory  and  is 
much  easier  prepared  than  by  the  old  method.  Its  comparative  value 
as  an  insecticide  must  be  left  to  the  entomologists  to  decide. 

Arsenical  Bordeaux. — 

Paris  Green _ _ 3^  to  1  lb. 

Bordeaux  Mixture _._ 100  gals. 


REPORTS   AND  BULLETINS  AVAILABLE  FOR  DISTRIBUTION. 


REPORTS. 


1896.  Report    of    the    Viticultural    Work    during    the    seasons    1887-93,    with    data 

regarding  the  Vintages  of  1894-95. 

1897.  Resistant    Vines,    their    Selection,    Adaptation,   and    Grafting.      Appendix   to 

Viticultural  Report  for  1896. 

1898.  Partial   Report  of  Work  of  Agricultural   Experiment   Station  for  the  years 

1895-96  and  1896-97. 
1900.     Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-1903. 

BULLETINS. 

Reprint.  Endurance  of  Drought  in  Soils  of  the  Arid  Region. 

No.  125.  Australian  Saltbush. 

128.  Nature,  Value,  and  Utilization  of  Alkali  Lands. 

129.  Report  of  the  Condition  of  Olive  Culture  in  California. 

131.  The  Phylloxera  of  the  Vine. 

132.  Feeding  of  Farm  Animals. 

133.  Tolerance  of  Alkali  by  Various  Cultures. 
135.  The  Potato-Worm  in  California. 

137.  Pickling  Ripe  and  Green  Olives. 

138.  Citrus  Fruit  Culture. 

139.  Orange  and  Lemon  Rot. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and   Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

143.  California  Peach-Tree  Borer. 

144.  The  Peach- Worm. 

145.  The  Red  Spider  of  Citrus  Trees. 

146.  New  Methods  of  Grafting  and  Budding  Vines. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant   Vines  and  their   Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

153.  Spraying  with  Distillates. 

154.  Sulfur  Sprays  for  Red  Spider. 

155.  Directions  for  Spraying  for.  the  Codling-Moth. 

156.  Fowl  Cholera. 

157.  Commercial  Fertilizers. 

158.  California  Olive  Oil ;  its  Manufacture. 

159.  Contribution  to  the  Study  of  Fermentation. 

160.  The  Hop  Aphis. 

161.  Tuberculosis  in  Fowls. 

162.  Commercial  Fertilizers. 

CIRCULARS. 

No.  1.  Texas  Fever.  No.  8.  Laboratory     Method     of     Water 

2.  Blackleg.  Analysis. 

3.  Hog  Cholera.  9.  Asparagus  Rust. 

4.  Anthrax.  10.  Reading     Course     in     Economic 

5.  Contagious  Abortion  in  Cows.  Entomology. 

6.  Methods  of  Physical  and  Chem-  11.  Fumigation  Practice. 

ical  Soil  Analysis.  12.     Silk  Culture. 

7.  Remedies   for   Insects. 

Copies  may  be  had  by  application  to  the  Director  of  the  Experiment 
Station,  Berkeley,  California. 


